The present invention relates generally to turbomachines and particularly, to damper pins and seal pins disposed between adjacent buckets on a rotor wheel.
As is well known, turbines generally include a rotor comprised of a plurality of rotor wheels, each of which mounts a plurality of circumferentially-spaced buckets. The buckets each typically include an airfoil, a platform, a shank and a dovetail, the dovetail being received in mating dovetail slot in the turbine wheel. The airfoils project into a hot gas path downstream of the turbine combustors and convert kinetic energy into rotational, mechanical energy. During engine operation, vibrations are introduced into the turbine buckets and if not dissipated, can cause premature failure of the buckets.
Many different forms of vibration dampers have been proposed to minimize or eliminate vibrations. Vibration dampers are often in the form of an elongated damper pins that fit between adjacent buckets and provide the damping function by absorbing harmonic stimuli energy produced as a result of changing aerodynamic loading. A damper pin is typically retained in a groove formed along one circumferentially-oriented “slash face” in the turbine blade shank region of one of each pair of adjacent buckets. The damping pin is centrifugally loaded during operation and, in order to prevent bucket-to-bucket binding, the groove must be machined so as to allow the pin to float relatively freely within the groove. At the same time, highly-compressed air is often extracted from the compressor of an axial turbine for the purpose of cooling turbine components, particularly those in the hot gas path downstream of the combustion. This cooling air is required to maintain the temperature of the turbine components at an acceptable level for operation, but comes at a cost to overall turbine efficiency and output. Any of the cooling flow that leaks out of the turbine components is essentially wasted. The pocket created by a damper pin groove provides a large leakage path for cooling flow to escape from the bucket shank region. The cooling efficiency can also be impaired by ingress of hot gas from the hot gas path into the bucket shank region.
In one prior arrangement, the damper pin has reduced-cross-section ends supported on shoulders formed in the bucket shank, with annular seals at the interfaces between the reduced-cross-section ends and the main body portion of the pin to minimize leakage along the damper pin groove.
For industrial gas turbines utilizing long bucket shank designs, a further approach to seal against cross-shank leakage is to provide radial seal pins between the shanks of adjacent buckets on the fore and aft sides of the shank, below the axially-extending damper pin. Like the damper pin, the radial seal pins are seated in seal pin grooves formed on the same slash face as the damper pin groove, and engage the substantially flat sides of the shank of the adjacent bucket. The sealing effectiveness of these cross-shank seals is an important factor in increasing the bucket life by minimizing thermal stress. Even when using both damper pins and radial seal pins, however, gaps remain between the radial seal pins and the reduced-cross-section ends of the axially-oriented damper pin, again creating readily-available leakage paths for hot combustion gases flowing past the buckets.
It would therefore be desirable to provide a more reliable sealing feature in order to prevent, minimize or control the escape of cooling flow from a pressurized shank cavity, prevent or minimize flow from leaking across the turbine blade from the forward wheel space to the aft wheel space in the case of a non-pressurized shank cavity, and/or to prevent ingress of hot gas path air into the shank region.